Relevant datas from WHO showed morbidity rate, disability rate, death rate of diabetes mellitus and overall health level of diabetes mellitus patients have already ranked the third place in non-infectious diseases, diabetes, together with tumors and cardiovascular diseases were the three main diseases which threats human health. Diabetes mellitus is usually classified into type 1 and type 2, there are more than 240 million diabetes patients, and 90% of them are suffering from type 2 diabetes, which also has a 1% growth rate every year, so, type 2 diabetes will be the main new growth point of diabetes drug market. The incidence of diabetes in China is about 5%, the number of patients of which ranks second place in the world just behind India. There are many antidiabetic drugs on the market, insulin injection, metformin, rosiglitazone, pioglitazone are representations of them. However, there is no drug alone can keep the HbAlc level of type 2 diabetes patients within the aimed range in a long term. Even though used in combination, the effect of the drugs will go down year by year after 3-4 years. Adverse reaction is one of the problems of many hypoglycemic drugs, wherein the fatal hypoglycemia is most worried by clinicians; secondly, many oral hypoglycemic drugs, such as sulfonylureas, α-glycosidase inhibitors and thiazolidinediones may all induce weight gain to patients, some of the drugs may also induce cardiovascular diseases.
Therefore, developing new type hypoglycemic drugs with brand new mechanism of action, higher safety and effectiveness is an important task that should be completed quickly for the scientists.
In the process of constantly finding new methods endocrine hormones were found to play an important role in the pathology and physiology of type 2 diabetes. Dipeptidyl peptidase-IV (DPP-IV) is an important enzyme related to diabetes, inhibiting the action of which to treat type 2 diabetes is a new method with good prospect. DPP-IV inhibitors can indirectly stimulate the secretion of insulin, the action of which is generated by inhibit DPP-IV to stabilize endocrine hormones such as incretin hormones, glucagons-like-peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP).
GLP-1 is a production expressed by glucagon protogene after eating, and mainly secreted by intestinal mucosa L-cell, and it can stimulate the secretion of insulin by pancreatic β-cells, which plays a significant role in the stability of blood sugar. Experiments prove that GLP-1 has physiological functions as following: acting on pancreatic β-cells in a glucose-dependent manner, facilitating the transcription of insulin genes, increasing the biosynthesis and secretion of insulin, stimulating the proliferation and differentiation of β-cells, inhibiting the apoptosis of β-cells to increasing the number of pancreatic β-cells; inhibiting the secretion of glucagon; inhibiting the appetite and food intake; retarding the emptying of gastric contents, etc., all of these functions are helpful to reduce blood sugar after food intake and to keep blood sugar within constant level. In addition, it won't cause the danger of severe hypoglycemia. GLP-1 well controlled the blood sugar of type 2 diabetes animal models and patients by multiple mechanisms. However, GLP-1 may lose biological activity through quick degradation by DPP-IV, and the half life of it is shorter than 2 minutes, which utterly limits the clinical use of GLP-1. It was found in researches that DPP-IV inhibitors can totally protect endogenous and even extraneous GLP-1 from inactivation by DPP-IV, improve activated GLP-1level, and reduce the antagonistic effect of GLP-1 metabolites. Moreover, DPP-IV inhibitors can also delay the incidence of diabetes through stimulating the regeneration of pancreatic β-cells and the improving the glucose tolerance and insulin sensitivity.
Dipeptidyl peptidase-IV (DPP-IV) inhibitors represent a novel class of agents that are being developed for the treatment or improvement in glycemic control in patients with Type 2 diabetes. For reviews on the application of DPP-IV inhibitors for the treatment of Type 2 diabetes, reference is made to the following publications: (1) H.-U. Demuth. et al. “Type 2 diabetes-Theraphy with dipeptidyl peptidase IV inhibitors”, Biochim. Biophvs. Acta. 1751:33-44 (2005) and (2) K. Augustyns. et al. “Inhibitors of proline-specific dipeptidyl peptidases: DPP4 inhibitors as a novel approach for the treatment of Type 2 diabetes”, Expert Opin. Ther. Patants, 15:1387-1407 (2005).
At present, some DPP-IV inhibitors have been disclosed (U.S. Pat. No. 5,462,928, U.S. Pat. No. 5,543,396, WO9515309, WO2003004498, WO2003082817, WO2004032836, WO2004085661), including MK-0431 as an DPP-IV inhibitor made by Merck which showed good inhibition activity and selectivity, and which has been on the market by 2006.

(R)-7-[3-amino-4-(2,4,5-trifluoro-phenyl)-butyryl]-3-trifluoromethyl-5,6,7,8-tetrahydro-imidazo[1,5-a]pyrazine-1-carboxylic acid methyl ester of the following formula is compound A, the code of which is SP2086.
